Electrode and interconnect materials for MEMS devices

ABSTRACT

A microelectromechanical (MEMS) device is presented which comprises a metallized semiconductor. The metallized semiconductor can be used for conductor applications because of its low resistivity, and for transistor applications because of its semiconductor properties. In addition, the metallized semiconductor can be tuned to have optical properties which allow it to be useful for optical MEMS devices.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS). More specifically, the invention relates to MEMS devices havingan electrical contact, electrode interconnect structures. One particularapplication can be found in capacitive MEMS devices. Finally, due to the(semi)-transparent nature of the electrode material in visible light,the invention also relates to optical MEMS devices, in general, andinterferrometric light modulators in particular.

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may have a pair of conductive plates, one orboth of which may be transparent and/or reflective in whole or part andcapable of relative motion upon application of an appropriate electricalsignal. In this type of device, one plate may be a stationary layerdeposited on a substrate and the other plate may be a metallic membraneseparated from the stationary layer by an air gap. The position of oneplate in relation to another can change the optical interference oflight incident on the interferometric modulator. Such devices have awide range of applications, and it would be beneficial in the art toutilize and/or modify the characteristics of these types of devices sothat their features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

One embodiment is a microelectromechanical system (MEMS) device,including a conducting electrode including a metallized semiconductor,and a movable element configured to be actuated by the conductor.

Another embodiment is a method of using a microelectromechanical system(MEMS) device, including applying a voltage to a conductor including ametallized semiconductor, where a movable element is actuated inresponse to the voltage.

Another embodiment is a method of manufacturing a microelectromechanicalsystem (MEMS) device, the method including forming a conductor includinga metallized semiconductor, and forming a movable element configured tobe actuated by the conductor.

Another embodiment is a microelectromechanical system (MEMS) device,including means for actuating a MEMS element, where the actuating meansis configured to partially transmit light and to partially reflectlight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIGS. 8A and 8B are cross-sections of an embodiment of a MEMS devicewith metal silicide, metal germanide, or metal germosilicide.

FIGS. 9A to 9D are cross-sections of the MEMS device shown in FIGS. 8Aand 8B at various stages in a manufacturing process.

FIG. 10 is a cross-section of an interferometric modulator with anelectrode comprising metal silicide, metal germanide, or metalgermosilicide.

FIGS. 11A to 11C are cross-sections of the interferometric modulator ofFIG. 10 and a transistor at various stages in a manufacturing process.

FIGS. 12A and 12B are graphs showing the reflectance of simulatedinterferometric modulators across wavelengths of visible light.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

Embodiments of the invention relate to MEMS devices that include aconductor made of a metallized semiconductor material. In oneembodiment, the MEMS device is an interferometric modulator with atransparent substrate, an electrode conductor and a movable mirror.Creating an electrical potential between the movable mirror and theelectrode conductor results in movement of the movable mirror towardsthe electrode conductor. In one embodiment, the electrode conductorcomprises a metallized semiconductor, such as a metal silicide, metalgermanide or metal germosilicide. By using such materials, the absorberlayer and conductor layer in a typical interferometric modulator can becombined into a single layer.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. Some examples ofsuitable materials include oxides, nitrides, and fluorides. Otherexamples include germanium (Ge), nickel silicide (NiSi), molybdenum(Mo), titanium (Ti), tantalum (Ta), and platinum (Pt). The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack are patterned intoparallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias). As is also illustrated in FIG.4, it will be appreciated that voltages of opposite polarity than thosedescribed above can be used, e.g., actuating a pixel can involve settingthe appropriate column to +V_(bias), and the appropriate row to −ΔV. Inthis embodiment, releasing the pixel is accomplished by setting theappropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 44, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one oremore devices over a network. In one embodiment the network interface 27may also have some processing capabilities to relieve requirements ofthe processor 21. The antenna 43 is any antenna known to those of skillin the art for transmitting and receiving signals. In one embodiment,the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE 802.11(a), (b), or (g). In anotherembodiment, the antenna transmits and receives RF signals according tothe BLUETOOTH standard. In the case of a cellular telephone, the antennais designed to receive CDMA, GSM, AMPS or other known signals that areused to communicate within a wireless cell phone network. Thetransceiver 47 pre-processes the signals received from the antenna 43 sothat they may be received by and further manipulated by the processor21. The transceiver 47 also processes signals received from theprocessor 21 so that they may be transmitted from the exemplary displaydevice 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 7E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.7C-7E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from its mechanicalproperties, which are carried out by the deformable layer 34. Thisallows the structural design and materials used for the reflective layer14 to be optimized with respect to the optical properties, and thestructural design and materials used for the deformable layer 34 to beoptimized with respect to desired mechanical properties.

FIGS. 8A and 8B show MEMS element 818 which operates as a switch. MEMSelement 818 comprises insulator 808, which is formed on substrate 820and supports a portion of mechanical layer 814. Electrode 812 is formedon substrate 820 so as to be spaced apart from mechanical layer 814 andis positioned between substrate 820 and mechanical layer 814 near aportion of mechanical layer 814 not supported by insulator 808. MEMSelement 818 also comprises terminal 810 formed on the substrate so as tobe positioned between substrate 820 and mechanical layer 814 near theunsupported end of mechanical layer 814.

Operation of the MEMS element is similar to that of the interferometricmodulator MEMS element described above. An electrical potential betweenmechanical layer 814 and electrode 812 generates an electromotive forcesuch that the mechanical layer 814 is attracted to electrode 812. Whenthe potential, and therefore attractive the electromotive force, islarge enough, mechanical layer 814 deflects towards electrode 812.Accordingly, the end of mechanical layer 814 approaches terminal 810.When the deflection of mechanical layer 814 is sufficient, mechanicallayer 814 contacts terminal 810 and an electrical connection isestablished between mechanical layer 814 and terminal 810.

After the electrical connection is established a signal driven ontomechanical layer 814 will be transmitted to terminal 810. Alternatively,after the electrical connection is established, a signal driven ontoterminal 810 will similarly be transmitted to mechanical layer 814.

Once the electrical connection between mechanical layer 814 and terminal810 is no longer needed, the electric potential between mechanical layer814 and terminal 810 may be reduced until the mechanical restorativeforce of mechanical layer 814 is greater than the attractiveelectromotive force between mechanical layer 814 and terminal 810. Inresponse to the greater restorative force, the mechanical layer 814returns towards a mechanically relaxed position not contacting terminal810. The electrical connection is broken and the switch is again openand non-conductive.

Electrode 812 and terminal 810 may comprise one or more metallizedsemiconductor materials such as, but not limited to, a metal silicide, ametal germanide, and a metal germosilicide (e.g. NiSi, CoSi₂, MoSi,CoSi, TaSi, TiSi, and Ni(Si_(x-1)Ge_(x))) in different crystallinephases and compositions. Metallized semiconductor materials comprise ametal and a semiconductor material such as, but not limited to silicon,germanium, gallium arsenide, Si_(x-1)Ge_(x), alloys, and SiC. A benefitof metallized semiconductors is shown in FIG. 8B, which illustrates MEMSboth element 818 of FIG. 8A and transistor 840 on substrate 820.Transistor 840 comprises gate electrode 837, gate oxide 835, drainelectrode 831, channel region 832, and source electrode 833. Transistor840 may be configured to directly or indirectly drive MEMS element 818,or may be configured to directly or indirectly sense a state of MEMSelement 818. The material used for electrode 812 and/or terminal 810 maybe similar to or substantially identical to that used for drainelectrode 831, channel region 832, and source electrode 833. In someembodiments, electrode 812, drain electrode 831, channel region 832, andsource electrode 833 are formed in substantially the same processingsteps.

FIGS. 9A through 9D are cross-sections of the MEMS element 818 andtransistor 840 at various stages in a manufacturing process. Thefollowing description is directed towards use of a semiconductormaterial. Such semiconductor materials include materials which comprise,for example, at least one of silicon, germanium, and gallium arsenide.These and various other materials with appropriate semiconductor andconductor properties may be used. FIG. 9A shows substrate 920 andsemiconductor layer 950 formed on substrate 920. At this point in themanufacturing process, semiconductor layer 950 may not substantiallycomprise metal. FIG. 9B shows semiconductor layer 950 after processingsuch that it is formed into electrode semiconductor 902, terminalsemiconductor 900, and transistor semiconductor 930. Transistor gateoxide 935 and transistor gate 937 are then formed over transistorsemiconductor 930, as shown in FIG. 9C. A metal is subsequentlydeposited over substrate 920. The metal may comprise at least one ofnickel, molybdenum, cobalt, tantalum, and titanium. Other metals mayalso be used. During a subsequent annealing process typically at300-900° C., some of the deposited metal integrates into the structureof the underlying electrode semiconductor 902, terminal semiconductor900, and transistor semiconductor 930. The resulting material isadvantageous for use both as a conductor, such as electrode 912 andterminal 910, and as transistor electrodes, such as gate electrode 937,drain electrode 933, and source electrode 931, as shown in FIG. 9C. FIG.9D shows insulator 908 and mechanical layer 914 fabricated by subsequentprocessing, so as to complete MEMS element 918.

As indicated above, a portion of both a transistor and a MEMS elementmay be substantially simultaneously fabricated. Because metallizedsemiconductor materials are useful for both conductor applications andtransistor electrode and channel applications, such simultaneousfabrication of different portions of a MEMS device is especiallyadvantageous, as these integrated devices can be provided with reducedmanufacturing complexity, size, and cost.

Another characteristic of metallized semiconductors is that, in additionto electrical and semiconductor properties, they have opticalreflectance properties which allow for advantageous use in optical MEMSdevices, such as interferometric modulator 1000, shown in FIG. 10. Whilethe following discussion is directed toward interferometric modulator1000, the aspects described herein are not limited to thisinterferometric modulator embodiment, and can be applied to any numberof other interferometric modulator embodiments, as well as any otheroptical MEMS device. Interferometric modulator 1000 of FIG. 10 issimilar in structure and function to the interferometric modulatorsshown in FIGS. 7C-7E. Interferometric modulator 1000 comprises electrode1016 formed on substrate 1020, insulator 1018 formed on electrode 1016,and reflective layer 1014 supported by deformable mechanical layer 1134formed above insulator 1018. Interferometric cavity 1010 is formedbetween electrode 1016 and reflective layer 1014. As described above,light λ is introduced to interferometric cavity 1010 through substrate1020, electrode 1016, and insulator 1018. Light of color and intensitydepending on interferometric properties of interferometric cavity 1016is reflected back through insulator 1018, electrode 1016, and substrate1020. Accordingly, the optical properties and the electrical propertiesof electrode 1016 both affect the performance of interferometricmodulator 1000.

Specifically, at least optical reflectance and electrical resistivityare parameters affecting the performance of interferometric modulator1000. Electrode 1016 provides an electrical function by serving as aconductor functioning to affect the position of reflective layer 1014 soas to adjust a primary dimension of interferometric cavity 1010, asdescribed above. In addition, electrode 1016 provides an opticalfunction by serving as a partially reflective layer, which defines afirst major boundary of interferometric cavity 1010, the other majorboundary being defined by the reflective layer 1014. In someinterferometric modulators, these two functions, electrical and optical,are provided by two separate layers. For example, transparent ITO (orother transparent conductive oxide, e.g. ZnO) may be used as theconductor functioning to affect the position of the reflective layer,and Cr may be used as a partially reflective layer, or absorber,defining a first major boundary of the interferometric cavity. However,in embodiments of this invention, a metallized semiconductor layer isused to combine and perform the functions of the ITO and Cr layers.Another benefit of using a metallized semiconductor for theelectrode/absorber is that the resistivity of metallized semiconductormaterials is lower than the resistivity of ITO, as is shown in thefollowing table:

RESISTIVITY OF VARIOUS MATERIALS Material Resistivity (μΩcm) ITO 120-500Nickel silicide 20-60 Molybdenum silicide ~100 Cobalt silicide 18-25Tantalum silicide 35-55 Titanium silicide 12-25

Accordingly, use of a metallized semiconductor allows for production ofthinner electrodes, while maintaining a desired low resistance. Forexample NiSi can be used to form an electrode which is from about 100 Åto about 500 Å. A MoSi electrode can be from about 200 Å to about 1000Å. A CoSi electrode can be from about 50 Å to about 200 Å, a TaSielectrode can be from about 80 Å to about 350 Å, and a TiSi electrodecan be from about 50 Å to about 200 Å.

The electrical and optical properties of the single metallizedsemiconductor layer can be tuned by the specific material used for themetallized semiconductor layer and by the thickness of the metallizedsemiconductor layer, its composition, crystalline phases and dopants.For example, given two metallized semiconductor layers of the samematerial and different thicknesses, the thicker layer will have lesselectrical sheet resistance (Ω/□) and greater optical reflectance incomparison to the thinner layer.

Additionally, given two metallized semiconductor layers of the samethickness and different materials, one will have greater opticalreflectance than the other and one will have greater electrical sheetresistance (Ω/□) than the other, according to the physical properties ofthe individual metallized semiconductor materials. Accordingly, byintelligent selection of material and thickness of the metallizedsemiconductor layer, the electrical and optical properties can be tunedto desired values. The following table shows resistivity (μΩcm) ofvarious metallized semiconductor materials.

Material Resistivity (μΩcm) TiSi₂ 13-16 ZrSi₂ 35-40 HfSi₂ 45-50 VSi₂50-55 NbSi₂  50 TaSi₂ 35-45 CrSi₂ ~600  MoSi₂ ~100  WSi₂ ~70FeSi₂ >1000  CoSi₂ 18-20 NiSi₂ ~50 PtSi 600-800 Pd₂Si 400

In addition, other processing parameters, such as, but not limited to,doping concentration, annealing temperature, and annealing time can beused to tune the electrical and optical properties of the metallizedsemiconductor layer.

In addition to a single metallized semiconductor layer providing bothelectrical and optical functions, an advantageous aspect of using ametallized semiconductor layer for the electrode/absorber is thatsemiconductor based electronic devices (e.g. transistors, capacitors,memory devices, and microprocessors) can be manufactured using some ofthe same processing steps as the interferometric modulator integrated onthe same substrate.

FIGS. 11A through 11C show a manufacturing process that can be used tosimultaneously manufacture a MEMS element 1100 and transistor 1140.FIGS. 11A through 11C are cross-sections of the interferometricmodulator 1000 and transistor 1140 at various stages in a manufacturingprocess. The following description is directed towards use of asemiconductor material. For example materials which comprise at leastone of silicon, germanium, and gallium arsenide may be used. However,any material with appropriate semiconductor and conductor properties maybe used. FIG. 11A shows substrate 1120 and semiconductor layer 1150formed on substrate 1120. At this point in the manufacturing processsemiconductor layer 1150 may not substantially comprise metal. FIG. 11Bshows semiconductor layer 1150 after processing such that semiconductorlayer 1150 is formed into electrode semiconductor 1106 and transistorsemiconductor 1130. Transistor gate oxide 1135 and transistor gate 1137are subsequently formed over transistor semiconductor 1130. A metal issubsequently deposited over substrate 1120. The metal may comprise atleast one of nickel, molybdenum, cobalt, tantalum, and titanium. Othermetals may also be used. During a subsequent annealing process, some ofthe metal integrates into the structure of the underlying electrodesemiconductor 1106 and transistor semiconductor 1130. The resultingmaterial is advantageous for use both as a conductor, such as electrode1116 and as transistor electrodes, such as gate electrode 1137, drainelectrode 1133, and source electrode 1131, as is shown in FIG. 11C. FIG.11C also shows insulator 1118, reflective layer 1114, and mechanicallayer 1134 fabricated by subsequent processing, so as to completeinterferometric modulator 1100.

As indicated, a portion of both a transistor and an interferometricmodulator may be substantially simultaneously fabricated. Becausemetallized semiconductor materials are useful for optical applications,conductor applications and transistor electrode applications, suchsimultaneous fabrication of different portions of an optical MEMS deviceis especially advantageous, as these various applications can beprovided with reduced manufacturing complexity, cost and device size.

In order to implement the simultaneous processing of a transistor and aMEMS element, such as those discussed above, the transistor and the MEMSelement may be may be manufactured or partially manufactured on a thinfilm transistor (TFT) or semiconductor production line.

TFT's are transistors in which the drain, source, and channel region ofthe transistor are formed by depositing a semiconductor over a basesubstrate. The semiconductor is appropriately patterned so as to definethe drain, source, and channel regions. Typically, the base substrate isa non-semiconductor substrate. See, e.g., “Thin FilmTransistors—Materials and Processes—Volume 1 Amorphous Silicon Thin FilmTransistors,” ed. Yue Kuo, Kluwer Academic Publishers, Boston (2004).The base substrate over which the TFT is formed may be anon-semiconductor such as glass, plastic or metal. The semiconductorthat is deposited to form the channel region of the TFT may, forexample, comprise silicon (e.g., a-Si, a-SiH) and/or germanium (e.g.,a-Ge, a-GeH), and/or gallium arsenide (e.g., a-GaAs), and may alsocomprise dopants such as phosphorous, arsenic, antimony, and indium.

Certain MEMS devices may be at least partially processed on a TFTproduction line simultaneously with certain TFT layers. For example, theMEMS device shown in FIG. 8B, comprising MEMS element 818 and transistor840, may be fabricated according to the process described with referenceto FIGS. 9A through 9D, where at least some of the fabrication isperformed on a TFT production line. For example, the processing aspectsdescribed with reference to FIGS. 9A through 9C may occur on a TFTproduction line, while the formation of insulator 908 and mechanicallayer 914 may be performed on a second production line. In someembodiments, the TFT production line may be modified so as to beadditionally capable of performing these fabrication steps.

EXAMPLE 1

An interferometric modulator comprising ITO as an electrode and Cr as anabsorber and an interferometric modulator comprising NiSi as a combinedelectrode/absorber were each simulated. Certain layers and layerthicknesses and optical performance simulation results are shown in thefollowing table:

COMPARISON OF DESIGNS WITH Cr/ITO AND NiSi Layer Cr/ITO design NiSidesign Electrode 500 Å (ITO) 200 Å (NiSi) Absorber 70 Å (Cr) No layerneeded Insulator 500 Å (Si0₂)/ 558 Å (Si0₂)/ 80 Å (Al₂O₃) 80 Å (Al₂O₃)Cavity (Bright/Dark) 1550 Å/0 Å 1255 Å/0 Å Reflective Layer (Al) 300 Å300 Å Mechanical Layer 1000 Å 1000 Å Optical Performance: Y 52 70 CR 3279 u′ v′ 0.155/0.468 0.171/0.470

FIGS. 12A and 12B show the reflectance of each of the simulatedinterferometric modulators across wavelengths of visible light.Comparing FIGS. 12A and 12B shows that the interferometric modulatorwith the metallized semiconductor has better optical performance atleast because it has higher reflectance across almost the entire band inthe bright state, and has lower reflectance across almost the entireband in the dark state.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the device or process illustrated may be made bythose skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A microelectromechanical system (MEMS) device, comprising: aconductor comprising a metallized semiconductor; and a movable elementconfigured to be actuated by said conductor, wherein the MEMS device isan optical MEMS device, and wherein the conductor comprises anelectrode, and the movable element moves in response to an electricalpotential between the conductor and the movable element, and theconductor has an electrical resistivity from about 10 μΩcm to about 100μΩcm and an optical reflectance from about 5% to about 40%.
 2. Thedevice of claim 1, wherein the metallized semiconductor comprises atleast one of metal one of silicon, germanium and gallium arsenide. 3.The device of claim 1, wherein the metallized semiconductor comprises atleast one of nickel, molybdenum, cobalt, tantalum, and titanium.
 4. Thedevice of claim 1, further comprising electronic circuitry configured toactuate the movable element, wherein the electronic circuitry comprisesa semiconductor.
 5. The device of claim 1, further comprising aninterferometric light modulation cavity between the movable element andthe electrode.
 6. The device of claim 1, wherein the electrode partiallytransmits light and partially reflects light.
 7. The device of claim 1,wherein the electrode has a thickness from about 5 nm to about 100 nm.8. The device of claim 1, further comprising electronic circuitryconfigured to actuate the movable element, wherein the electroniccircuitry comprises a semiconductor.
 9. The device of claim 1, furthercomprising: a display; a processor configured to communicate with thedisplay, the processor configured to process image data; and a memorydevice configured to communicate with the processor.
 10. The device ofclaim 9, further comprising a driver circuit configured to send at leastone signal to the display.
 11. The device of claim 10, furthercomprising a controller configured to send at least a portion of saidimage data to the driver circuit.
 12. The device as recited in claim 9,further comprising an image source module configured to send the imagedata to the processor.
 13. The device of claim 12, wherein the imagesource module comprises at least one of a receiver, transceiver, andtransmitter.
 14. The device as recited in claim 9, further comprising aninput device configured to receive input data and to communicate theinput data to the processor.
 15. A method of using amicroelectromechanical system (MEMS) device, comprising: applying avoltage to a conductor comprising a metallized semiconductor, wherein amovable element is actuated in response to the voltage, the conductorhaving an electrical resistivity from about 10 μΩcm to about 100 μΩcmand an optical reflectance from about 5% to about 40%.
 16. The method ofclaim 15, wherein the metallized semiconductor comprises at least one ofsilicon, germanium and gallium arsenide.
 17. The method of claim 15,wherein the metallized semiconductor comprises at least one of nickel,molybdenum, cobalt, tantalum, and titanium.
 18. The method of claim 15,further comprising applying a voltage to electronic circuitry configuredto actuate the movable element, wherein the electronic circuitrycomprises a semiconductor.
 19. The method of claim 15, furthercomprising modulating light.
 20. The method of claim 15, furthercomprising interferometrically modulating light based at least in parton an electrical potential between the conductor and the movableelement.
 21. The method of claim 15, further comprising partiallytransmitting light through the conductor and partially reflecting lightfrom the conductor.
 22. The method of claim 15, further comprisingapplying a voltage to electronic circuitry configured to actuate themovable element, wherein the electronic circuitry comprises asemiconductor.
 23. A method of manufacturing a microelectromechanicalsystem (MEMS) device, the method comprising: forming a conductorcomprising a metallized semiconductor; the conductor having anelectrical resistivity from about 10 μΩcm to about 100 μΩcm and anoptical reflectance from about 5% to about 40%; and forming a movableelement configured to be actuated by said conductor.
 24. The method ofclaim 23, wherein forming the conductor is performed on a firstproduction line configured to produce thin film transistors.
 25. Themethod of claim 24, wherein forming the movable element is performed ona second production line.
 26. The method of claim 24, wherein formingthe movable element is performed on the first production line.
 27. Themethod of claim 23, wherein the metallized semiconductor comprises atleast one of metal one of silicon, germanium and gallium arsenide. 28.The method of claim 23, wherein the metallized semiconductor comprisesat least one of nickel, molybdenum, cobalt, tantalum, and titanium. 29.The method of claim 23, further comprising forming electronic circuitryconfigured to actuate the movable element, wherein the electroniccircuitry comprises a semiconductor.
 30. The method of claim 23, furthercomprising configuring the device to modulate light.
 31. The method ofclaim 23, further comprising configuring the device tointerferometrically modulate light based at least in part on anelectrical potential between the conductor and the movable element. 32.The method of claim 23, further comprising forming an interferometriclight modulation cavity between the movable element and the conductor.33. The method of claim 23, further comprising configuring the conductorto partially transmit light and to partially reflect light.
 34. Themethod of claim 23, further comprising forming the conductor with athickness from about 5 nm to about 100 nm.
 35. The method of claim 23,further comprising forming electronic circuitry configured to actuatethe movable element, wherein the electronic circuitry comprises asemiconductor.
 36. A microelectromechanical system (MEMS) device madeaccording to the method of claim
 23. 37. A microelectromechanical system(MEMS) device, comprising: means for actuating a MEMS element, whereinthe actuating means is configured to partially transmit light and topartially reflect light, and the actuating means is configured toreflect from about 5% to about 40% of incident light.
 38. The device ofclaim 37, wherein the actuating means comprises a conductor comprising ametallized semiconductor.